Vulcanization of rubber



Patented Apr. 3, 1945 VULC-ANIZATION OF RUBBER Marion W. Harman, Nitro, W. Va., assignor-to Monsanto Chemical Company, St. Louis, Mo., a

corporation of Delaware No Drawing. Application April 27, 1943, Serial No. 484,782

18 Claims.

The present invention relates to a new and improved class of rubber vulcanization accelerators, to a process of vulcanizing a rubber or a rubber containing material and to the vulcanized rubber products obtained with the aid of the new accelerators.

The accelerators of the present invention comprise N-cyano alkyl substituted dithiocarbamic acids and their derivatives. In accordance with this invention it has been discovered that compounds containing the grouping where R is an alkylene group and R is an alkyl group are valuable accelerators. The alkyl roup may be of the straight chain type or the alicyclic type as for example cyclohexyl or an aryl substituted alkyl group as for example benzyl or other group having an alkyl carbon atom attached to the nitrogen atom. Since the free dithiocarbamic acids are unstable substances they are used in the form of their derivatives particularly pri mary, secondary and tertiary amine salts, metallic salts, thiuram monosulfides, disulfides and polysulfides. I

Carbon disulfide combines readily with cyano' Y substituted secondary alkyl amines to form cyano alkyl substituted secondary amine salts of the cyano alkyl substituted dithiocarbamic acid. If the reaction is carried out in the presence of a tertiary amine, as for example N-N-dimethyl cy 1 clohexyl amine, a tertiary amine salt is formed and in the presence of alkali metal hydroxide the alkali metal salts are formed These too are useful accelerators. Particularly valuable are the heavy metal salts, as for example zinc and lead salts, and thiuram sulfides. The former are precipitated upon'the'addition of a soluble salt of the heavy metal to an aqueous alkaline solution of the dithiocarbamic acid. 'I'hiuram disulfides are prepared by-oxidation in aqueous alkaline solution of the dithiocarbamic acids and the thiuram monosulfides result from the removal of one atom of sulfur from the thiuram disulfide in known manner. Thiuram polysulfides may be prepared by the-action of sulfur chlorides on the dithio carbamic acids. Obviously; other methods of syn-- thesis may be employed where convenient or de-' sirable and this invention is not limited to the process by which the new acceleratorsare'manu factured.

Typical examples of the new accelerators which illustrate the invention but are not to be taken as limiting the invention are the amine and metallic salts, andthe-thiuram sulfides fromthe following dithiocarbamic'acids: N-fi-cyan'o ethyl, N-methyl dithiocarbamic acid; N-. 8.'cyano ethy N-ethyl dithiocarbamic acid; N-B-cyano n-propyl, Neethyl dithiocarbamic acid; ,N-B cyanoisopropyl, N-ethyl dithiocarbamic acid; N-fi cyano ethyl, N-n-propyl dithiocarbamic acid; N-fl-cyano ethyl, N-isopropyl dithiocarbamic acid; N-B- cyano n-propyl, N-n-propyl dithiocarbamic acid; N-c-cyano isopropyl, N-ispropyl dithiocarbamic acid; N-B-cyano ethyl, N-n-butyl dithiocarbamic acid; N-B-cyano ethyl, N-sec. butyl dithiocarbamic acid; N-p-cyano ethyl, N-tertiary butyldithiocarbamic acid; N-B-cyano ethyl, N-isobutyl ditb ocarbamic ac d; N-B-cyano,n-p1"opyl, N-n butyl dithiocarbamic acid; N fl-cyano ethyl, N-n-' amyl dithiocarbamic acid; N-fi-cyano ethyl, N-

isoamyl dithiocarbamic acid; N-p-cyano ethyl, N-tertiary amyl dithio'carbamic acid; N-fl-cyano ethyl, N-hexyl dithiocarbamic acid; N-fi-cyan'o ethyl, N-octyl dithiocarbamic acid; N-B-cyano ethyl, N-n-nonyl dithi'ocarbamic acid; N +p-cyano' ethyl, N-Z-nonyl dithiocarbamic acid; N-fi-cyano ethyl, N-decyl dithiocarbamic acid; N-fi-cyano ethyl, N-n-undecyl dithiocarbamic acid; N-pcyano ethyl, N-2-undecyl dithiocarbamic acid; N-c-cyano ethyl, N-dodecyl dithiocarbamic acid; N-o-cyano ethyl, N-pentadecyl dithiocarbamic acid; N-B-cyano n-propyl, N-allyl dithiocarbamicacid; N-c-cyano isopropyl, N-fi-hydroxy ethyl dithiocarbamic acid; N-cyano methyl, N-fl-hy droxy ethyl dithiocarbamic acid; N-m-cyano nbutyl, N-B-hydroxy' n-pr'opyl dithiocarbamic acid; N-B-cyano i'sopropyl, N-benzyl dithiocar-. bamic acid; N-B-cyano ethyl, N-chlorbenzyl dithiocarbamic acid; di(N-fi-cyano ethyl) dit-hio-- carbamic acid and equivalents and analogues thereof.

An important group of cyano substituted sec-. ondary alkyl amines useful for the preparation of the new accelerators can he prepared from primary alkyl amines-and unsaturated open'chain nitriles as described in United States Patent No.

1,992,615 granted to Hofimann et al. The method comprises mixing equimolecular proportions of an unsaturated open chain nitrile and a primary alkyl amine or reacting two molecular proportions of an unsaturated nitrile with ammonia. Other methods of synthesis are described in United States Patent No. 1,972,465 granted to Ulrich et al. The following examples illustrate the preparation of the new accelerators but again are not to be taken as limitative of the invention.

Into a suitable container fitted with a reflex condenser there was charged substantially 304 parts by weight of p-cyano ethyl cyclohexyl amine (substantially two molecular proportions) and substantially 76 parts by weight of carbon disulfide (substantially one molecular proportion). An exothermic reaction set in immediately. The product was an amber resin believed to be the N-p-cyano ethyl N-cyclohexyl amine salt of N-p-cyano ethyl N-cyclohexyl dithiocarbamic acid. The yield was substantially quantitative or 380 parts by weight. In similar manner were prepared the N- 8cyano ethyl, N-n-butyl amine salt of N-c-cyano ethyl, N-n-butyl dithiocarbamic acid; the N-fi-cyano ethyl, N-ispropyl amine salt of N-p-cyano ethyl, N-isopropyl dithiocarbamic acid; the N-B-cyano ethyl, N-namyl amine salt of N-fi-cyano ethyl, N-n-amyl dithiocarbamic acid; the N-fi-cyano ethyl, N-allyl amine salt of N-fl-cyano ethyl, N-allyl dithiocarbamic acid and the N-B-cyano ethyl, N-dodecyl amine salt of N-fl-cyano ethyl, N-dodecyl dithiocarbamic acid. The products were syrupy liquids and were obtained in substantially quantitative yield. On standing the p-cyano ethyl, dodecyl amine derivative set to a Jelly and the B-cyano ethyl ispropyl amine derivative crystallized to a soft solid.

Into a suitable container fitted with a reflux condenser there was charged substantially 83.5 parts by weight (substantially 0.6 molecular proportion) of aqueous 33% ethyl amine and substantially 32.5 parts by weight (substantially 0.6 molecular proportion) of acrylonitrile. The nitrile was graduallyadded tothe amine at 10-15 C. upon which, an exothermic reaction set in. The charge was stirred for a short time at room temperature and substantially 23 parts by weight of carbon disulfide (substantially 0.3 molecular proportion) added to the clear colorless solution. The water and any unreacted carbon disulfide were removed by evaporation or other means leaving a residue of viscous yellow resin in nearly quantitative yield'believed to be the N-e-cyano ethyl N-ethyl amine salt of N-s-cyano ethyl N- ethyl dithiocarbamic acid.

Into a suitable container fitted with a reflux condenser there was charged substantially 42.8

parts by weight of benzyl amine and substantially 21.2 parts by weight of acrylonitrile (substantially 0.4 molecular proportion of each). The charge was heated at 100-110 C. for about an hour, cooled below 50 C. and 15.2 parts by weight (substantially 0.2 molecular proportion) of carbon disulfide added while keeping the temperature below 50 C. The product was a clear brittle resin believed to be the N-B-cya'no ethyl N-benzyl amine salt of N-B-cyano ethyl N-benzylclithiocarbamic acid. The yield was nearly quantitative.

Into a suitable reaction vessel fitted with a reflux condenser there was charged 53 parts by weight of acrylonitrile (substantially one molecular proportion) and substantially 50 parts by weight of aqueous 60% ethylene diamine (substantially 0.5 molecular proportion). The temperature was kept below 60' C. and after the strong exothermic reaction had subsided, the charge was stirred until it had cooled to room temperature. Substantially equimolecular proportions of the di(N-s-cyano ethyl) ethylene diamine so obtained and carbon disulfide were mixed keeping the temperature below 50 C. A viscous yellow oil formed immediately which set up to a clear resin. This product was believed to be an inner salt of N-s-cyano ethyl N-p-(pcyano ethyl) amino ethyl dithiocarbamic acid, presumably of the structure An aqueoussolution of the sodium salt of N- ,a-cyano ethyl N-n-butyl dithiocarbamic acid was prepared by mixing with cooling substantially 31.5 parts by weight (0.25 molecular proportion) of N-p-cyano ethyl N-n-butyl amine, 40 parts by weight of 25% sodium hydroxide, 125 parts by weight'of water and 19 parts by weight (substantially 0.25 molecular proportion) of carbon disulfide. The temperature was kept at 2030 during the reaction and the thiuram sulfide prepared by slowly adding to the clear yellow solution with further cooling an oxidizing mixture consisting of 16.9 parts by weight of 26.6% hydrogen peroxide, 13.1 parts by weight of 66 sulfuric acid and 125 parts by weight of water. The temperature was kept at 1015 C. during the oxidation. A viscous brown syrup separated from which the aqueous layer was decanted and the syrup washed with water, taken up in ether or other solvent, dried and the solvent evaporated. The viscous syrupy residue obtained in about yield was believed to be di(N-,9-cyano ethyl N-nbutyl) thiuram disulfide. Sulfur calculated for C16H26N4s4 31.8%; found 30.1%. Nitrogen ca1- culated 13.9%; found 14.2%.

Substantially 36 parts by weight (substantially 0.125 molecular proportion) of ZnSOMHzO in 250 parts by weight of water was added to an aqueous solution containing 0.25 molecular proportion of the sodium salt of N-p-cyano ethyl N-n-butyl dithiocarbamic acid prepared as described above. The zinc salt precipitated in nearly quantitative yield as a soft colorless solid.

In similar manner the zinc salt of N-p-cyano ethyl N-methyl dithiocarbamic acid was prepared byprecipitatingwith zinc sulfate from an aqueous solution of the sodium salt. The product was a cream colored solid. The zinc salt of N-p-cyano ethyl N-cyclohexyl dithiocarbamic acid prepared in the same manner was a voluminous white powder. Analysis for sulfur, nitrogen and zinc gave values of 25.15%, 10.88% and 12.76% respectively. The required values for and zinc Substantially 15.2 parts-by weight of cyclohexylamino propionitrile B. P. l27/7 mm. obtained by the reaction of cyclohexylamine and propionitrile (substantially 0.1 molecular prosides and bottom of the container.

portioniand substantially 12.7 parts by weight of N,N dimethyl cyclohexylamine (substantially 0.=1 molecula r -proportion:) were'charged into a glass o r 'glas's lined vessel of suitable capacity and dissolved in ether or other solvent. The solution was cooled to 20-30 C. and 7.6'parts byweight of. carbon disulfide (substantially 0.1 molecular proportion) added thereto. After standing a short time crystals began to deposit on the The solution was cooled to 15 0.. the crystalline product filtered ofi, washed with ether and dried. Snow white crystals M. P. 103-104 were obtained. Analysis for sulfur and nitrogen gave 18.00% sulfur"and.'l 2;05% nitrogen. The calculated values for the N,N-dimethyl cyclohexylamine salt of N- c-cyano; ethyl N-cyclohexyl dithiocarbamic acid are 18.03% sulfur and 11.83%- nitrogen.

Substantially 54.5 parts by weight of 90% so dium cyanide was dissolved in substantially 100 parts by..welght of water and the solution cooled to 5-10" C. 166 par-ts by weight of approximate- 1y 30% sulfuric acid was added slowly, keeping the-temperature below C. 73 parts by weight of;butyl amine (substantially one molecular proportion) was added and then 81.8 parts by of 365.7% formaldehyde. The temperature was kept at, 5-15" C. throughout the addition of these re agents. The charge was heated'ior one hour at 50 0., cooled -to 10 C. and the upper organlc layer poured off and dried over anhydrous sodium sulfate. The oil was distilled collecting the fraction boiling at '7780' C. at 6 mm. A water white oil was obtained which was found to contain 25.08% nitrogen. The value calculated-for N-cyano methyl butyl amine was 25.00% nitrogen.

Substantially 22.4 parts by weight of N-cyano methyl-butyl amine 32 parts by weight 01 25% caustic soda and 250 parts by weight of water were charged into a vessel of suitable capacity and the charge cooled to C. Substantially 152 parts by weight of lcarbondisulfide was then added keeping the temperature at 15-25 C. After the carbon disulfide had entered into reaction an aqueous solution containing 18.1 parts. by weight of 89% zinc sulfate was added. white powder precipitated which was filtered off and. dried in an oven. The product was believed to be the zinc salt of N-cyano methyl N-butyl" dithiocarbamic acid. I Substantially 22.4 parts by weight of N-p-cyano isopropyl N ethyl amine B. F. 77-78/14 mm. (Bull. Soc. Belgique 32. 256 (1923)) and 32 parts by weight of 25% caustic soda (substantially 0.2. molecular proportions of each) and 250 parts by weight of water were charged. into a'vessel' of suitable capacity. Substantially 15.2 parts by weight (0.2 molecular proportion) of carbon 'disulfide was added and the charge stirred for about. three hours. A dilute aqueous solution contain-'= ing 18. 1 parts by weight of 89% .zinc sulfateisubsta'z'itially 0.1 'i'nolecular proportion) was added.- A precipitate formed which was v filtered, 0.1T. washed free of sulfates and dried. A pale yellow powderwas obtained believed to be thezincisalt. of N- Bscyano isopropyl N-ethyl dithiocarbamim acid.

.Parts byweight Buna S ,mbber.is-vermin 1.00 Carbonrblackgucufi '50 Zinc oxide 5 Sulfur 2 S-tearic acid 0.5 Accelerator 0.5

1 Buna S is the copolymer of butadiene-1,3 and styrene.

In this manner stocks were compounded containing as the accelerator Stock Accelerator 15 N-fi-cyano ethyl N-n-butyl amine salt of N-fl-cyano ethyl N-n-butyl dithiocarbamic acid. B. N-fi-cyauo ethyl N-cyclohexyl amine salt of N-B-cyano ethyl N- cyclohexyl dithioearbamic acid. C N-B-cyano ethyl N-B-hydroxy ethyl amine salt of 'N-fi hydroxy ethyl N-fl-cyano ethyl dithiocarbamic acid. I) Inner salt Oi-N-fi-cyano ethyl, N-B-(fl-cyauo ethyl) amino ethyl dithiocarbamic acid.

E. N-B-cyano ethyl N-methyl amine salt of N-B-cyano ethyl N -methy1 dithiocarbamic acid. F N-B-cyano ethyl N -ethyl amine salt of N-fi-cyano ethy- N-ethyl .dithiocarbamic acid. G N-fi-cyano ethyl N-allyl amine salt of N-fi-cyano ethyl,

N-allyl dithiocarbamie acid. H N-B-cyano ethyl N-benzyl amine salt of N-fi-cyano ethyl,

N-benzyl dithiocarbamic acid. J N-B-cyano ethyl N-dodecyl amine salt of N-fl-cyano ethyl N -dodecyl dithiocarbamic acigl. K N-fl-cyano ethyl N-isopropyl amine salt of N-fl-cyano ethyl N-isopropyl dithiocarbamic acid. L. N-B-cyano ethyl N-n-amyl amine salt of N-B-cyano ethyl N-n-amyl dithiocarbamic acid. l

The stocks so compounded were cured .by heating for different periods of time in apress at the temperature of pounds steam pressure per 35 square inch. The modulus and tensile properties of the 180 minute cure are set forth below to illustrate the accelerating properties.

0 Modulus of 4 elasticity Tensile at Ultimate Stock at 400% break in elongation,

elongation lbs/in." per cent in lbs/in.

The examples given below illustrate the acceleratingactlon of the new compounds and are not to be considered as limiting the invention.

"As specific embodiments of the invention typical members of the new class ofaccelerators were incorporated into the'formula comprising In general, the new accelerators of this invention are characterized by the absence of scorch or pre-vulcanization of the rubber stocks in which they are incorporated. Thus, uncured stocks were tested with a Williams plastometer described by Williams, Industrial and Engineering Chemistry for 1924, vol. 16, p. 362-see also Krall ibid., vol. 16, p. 922. Samples of uncured stock were heated at 121 C. and the time required for the stock to show a set-up or scorch was determined. Typical data areset forth below:

Hours heat, Stock ing to scorch This data shows that the rubber-stocks contain ing the new accelerators are resistant to pre-- 1 vulcanization. A similar stock containing a commercial accelerator noted for its marked delayed action set-up in 4 hours.

As further specific embodiments of the invention other stocks were compounded comprising:

Stock N O P Parts by weight Buna S rubber Stearic acid Di (N-B-cyano ethyI N- n-butyl) thiuram disulfide Di (N-fl-cyano ethyl N- cyclohexyl) thiuram disuliide Zinc N-B-cyano ethyl,

N-methyl dithiocarbamate Zinc N-fl-cyano ethyl,

N -cyclohexyl dithiocarbamate Zinc N-B-cyauo ethyl,

N-n-butyl dithiocarbamaic. l I

The stocks so compounded were cured in the usual manner by heating in a press at the temperature of 45 pounds steam pressure per square inch. The modulus and tensile properties of the cured products are set forth below.

Modulus of Cure elasticity at Tensile at Ultimate Stock time in 400% elongabreak in elongation,

mins. tion in lbs/in. per cent lbs./in.

The foregoing data show that the new compounds possess desirable accelerating action.

As further illustrative of the invention stocks were compounded comprising The stocks so compounded were cured in the usual manner by heating for different periods of time in a press at the temperature of 45 pounds of steam pressure per square inch.

Modulus of Cure elasticity at Tensile at Ultimate Stock time in 400% elongabreak in elongltlom.

mins. tion in lbs./in 1 percent lbs/in! Buna S rubber when employed in a formula containing a high sulfur ratio.

As further illustrative of the invention stoclrs' were compounded comprising Stock W X Y Parts by Paris by Paris by weight weight weight Hycar 0R rubber l 100 100 Gastex 50 50 50 5 5 5 1. 5 1. 5 1. 5 1. 0 1. 0 l. 0 N-fl-cyano ethyl N -but 1 amino salt of N-B-cyano ethy N-butyl dithiocarbamic acid 0.3 N-fi-cyano ethyl N cyclohexylamine salt of N-fi-cyano ethyl N-cyclohexyl dithiocarbamic acid. 0. 3 N-B-cyano ethyl N -fl-hydroxy ethyl amine salt of N-flbyano ethyl N- B-hydroxy ethyl dithiocarbamic acid 0. 3

Hycar OR is the copolymer of butadiene-l,3 and ecrylonitnla,

The stocks so compounded were cured by heating in a press at the temperature of 60 pounds steam pressure per square inch.

Modulus of v Cure elasticity Tensile at Ultimate Stock time in at 400% break in elongation,

' mins. elongation lbs/in. per cent in lbs./in.

These results show that the new compounds are valuable accelerators for use in Hycar OR. As further specific embodiments of the invention the new compounds were incorporated in an india rubber formula comprising Di(N-B-cyano ethyl N-n-butyl) thiuram disulfide.

D l(N-B-eyano ethyl N'cyelohexyl) thiuram disulfilie. Zinc N-B-cyano ethyl, N -methyl dithiocarbamate.

Zinc N -fl-cyano ethyl, N-n-butyl dlthiocarbamate.

N,N dimethyl cyclohcxyl amine salt of N-cyclohcxyl N-B-cyano ethyl dithiocarbamic acid.

N-fl-cyano ethyi,N-n-butyl amine salt of N-fi-cyann ethyl, N -n-butyl ditbiocarbamic acid.

ethyl, N -cyclohexyl dithiocarbamic acid.

Zinc N-B-cyano ethyl, N-cyclnhcxyl dithiocarbamate.

N-B-cyano ethyl, Ncyclohexyl amine salt of N-B-cyanii 2,379,895 I l The stocks so compounded were cured in the. usual manner by heating for different periods of time in: a press at the temperature of 30 pounds steam pressure per square inch.

Modulus of Cure elasticity at Tensile at Ultimate Stock time in elongation break in elongation, mins. of 500% lhst/in. per cent in lbs/m These results show that the new accelerators possess strong accelerating action in typical india "rubber formulas.

' The preferred compounds function as valuable Stock A-l A-2 A3 A-4 Butyl rubber 100 100 100 100 Carbon black. 50 50 50 50 Zinc oxide. 5 5 5 5 Stearic acid. 3 3 3 3 Sulfur 1. 5 1. 5 1. 5 1. 5 Zinc salt of N -B-cyano ethyl N-n-butyl dithiocarbamio acid 1.0 Zinc salt of N-B-cyano ethyl N -cyclohexyl dithiocarbamic acid... 1.0 Di(N-B-cyano ethyl, N-cycloh ram disulfide l. 0 N- -cyano ethyl, N -isopropyl amine salt of N -B-cyano ethyl N -isopropy1 dithiocarbamic acid 1. 0

The stocks so compounded'were vulcanized in the usual manner by heating in a press at the temperature of 60 pounds of steam pressure per square inch (307 F).

The above data show the valuable accelerating action of the new compounds in butyl rubber.

In another specific example of the invention a stock was compounded comprising The softener was the condensation product of three molecular proportions of acetone with one molecular proportion ofethanol amine and an aromatic type hydrocarbon softener in equal proportions;

The-stockso compounded Was given a-dry heat cure by placing itin a bomb under 25 pounds air pressure per-square inch and; heating at 287 R101 45 minutes. The physical properties of the carbamate cured product were as follows:

Modulus'or elasticity in Tensile at Ultimate Stock lbs/in. at break in elongation, elongation lbs/in. per cent The above data show that the new accelerators may be'used with other type accelerators as activators thereof andfurther that they are useful for accelerating vulcanization by dry heat.

Stocks were compounded comprising Stock Parts by Parts by weight weight Smoked sheets rubber 100 Carbon black 50 50 Zinc oxide 5 5 Sulfur. 3 3 Pine tar 2 2 Stearic aci 3 3 Condensation product of acetone and p-amino 1p eny Zinc N-fi-cyano isopropyl N-ethyl dithio- The stocks so compounded were cured in the usual manner by heating in a press at the temperature of 30 pounds steam pressure per square inch.

i d tie Cure y m Tensile at Ultimate Stock time in at elongatmns break in elongation,

mins. lbs/in. per cent The above data show the strong accelerating action typical of the preferred class of compounds.

Zinc N-cyano methyl N-butyl dithiocarba mate 1.0

The stock so compounded was cured by heating in a press at the temperature of 40 pounds of steam pressure per square inch.

The above data illustrate the accelerating action of accelerators in which the alkylene group of the cyano alkyl substituent is a methylene group.

The term "a rubber as used in the attached claims-is meant to include a sulfur vulcanizable plastic material which possesseshigh extensibility 7 under load coupled with the property of forcibly retracting to approximately its original size and shape after the load is removed. Examples are india rubber, reclaimed rubber, balata, gutta percha and other natural or synthetically prepared sulfur vulcanizable products.

The present invention is not limited to the specific examples hereinbefore set forth wherein the new accelerators are preferred. Other ratios of the compounding ingredients than those mentioned in the examples as well as otherwell known fillers, pigments and the like may be employed in the production'of various types of rubber compounds as will be apparent to those skilled in the art to which this invention pertains. This invention is limited solely by the claims attached hereto as part of the present specification.

What is claimed is:

1. The process of vulcanizing a rubber which comprises heating a rubber and sulfur. in the presence of a compound containing the grouping GN-R s I Ncsr."

where R is an alkylene radical, R is an alkyl radical and R represents a substituent of the class consisting of the radical and metallic salt forming radicals.

2. The process of vulcanizing a rubber'which comprises heating a rubber and sulfur in the presence of a compound containing the grouping CNCHr-CH: s

Nt -sM R where R is an alkyl radical and M is a heavy metal salt forming element. 1.

3. The process of vulcanizing a rubber which comprises heating a rubber and sulfur in the presence of a compound containing the grouping where R is an alkyl radical.

4. The process of vulcanizing a rubber. which comprises heating a rubber and sulfur in the 1 where R, is an alkyl radical.

5. The process of vulcanizing a rubber which comprises heating a rubber and sulfur in the presence of a zinc salt of compound containing the grouping where R is an alkyl radical.

6. The process of vulcanizing a rubber whi ch where R is a hydrocarbon radical containing more than one carbon atom and having an alkyl carbon atom linked to the nitrogen. I

'7. The process of vulcanizing a rubber which comprises heating a rubber and sulfur in the presence of a compound containing the grouping 8. The process of vulcanizing a rubber which comprises heating a rubber. and sulfur in the presence of the zinc salt of N-fl-cyano ethyl N- butyl dithiocarbarnic acid.

9. The process of vulcanizing a rubber which comprises heating a rubber and'sulfur in the presence of the zinc salt of N- B-cyano ethyl N- cyclohexyl clithiocarbamic acid.

10. The vulcanized rubber product obtained by heating a rubber and sulfur in the presence 0 a compound containing the grouping CN--R s N-(L-S-R where R is an valliylene radical, R is an alkyl radical and R" represents a substituent of the class consisting of the radical and metallic salt forming radicals. I

heating a rubber and sulfur in the presence of asalt of a dithiocarbamic acid containing the grouping CN-CHr-CH: NC-SH where R. is an alkyl radical.

14. The vulcanized rubber product obtained by heating a rubber and sulfur in the presence of a zinc salt of compound containing the grouping CN-CHa-CH: 8

R where R is an alkyl radical.

15. The vulcanized rubber product obtained by heating a rubber and sulfur in the presence of a compound containing the grouping where R is a hydrocarbon radical containing inore than one carbon atom and having an alkyl carbon atom linked to the nitrogen.

16. The vulcanized rubber product obtained by heating a rubber and sulfur in the presence of a compound containing the grouping CN-CHz-CH: S 3 CHr-CH:CN

C4119 04KB 17. The vulcanized rubber product obtained by heating a rubber and sulfur in the presence of the zinc salt of N-e-cyano ethyl N-butyl dithiocarbamic acid.

18. The vulcanized rubber product obtained by heating a rubber and sulfur in the presence of the zinc salt of N-p-cyano ethyl N-cyclohexyl dithiocarbamic acid.

MARION W. HARMAN. 

